Field of the Invention
The present invention relates to a liquid crystal display.
Description of the Background Art
In recent years, as the semiconductor technology progresses, development has been proceeding on the information systems and the information devices having higher performance, and there, the image has been playing an increasingly important role as a human interface. As the human interfaces, information displays that display information are utilized in various situations, leading to a demand for higher-performance and higher-quality information displays. Particularly in liquid crystal displays (LCDs) including the constituent components that are in a liquid state and thus can be easily deformed, keeping the uniformity of liquid crystal layer is an important challenge.
One example of the human interfaces is a device that includes an input unit such as a touch panel disposed on the front surface of a liquid crystal display and is operated by a user touching a display screen, and such a device has been widely used. In the above device, when a user touches the display screen, an external force (pressing force) is applied onto the liquid crystal display in some cases. Even in such a case, the uniform displaying needs to be kept without causing interference with the display characteristics.
In a liquid crystal display such as the one described above, the liquid crystal cell in which liquid crystals are sandwiched between the substrates disposed to be opposed to each other often has the structure in which a number of the columnar spacers (also referred to as post spacers (PSs)) formed by photolithography are aligned in the cell, to thereby hold the gap between the substrates. The columnar spacers are expected to keep the thickness of the liquid crystal layer (corresponding to the gap between the substrates and hereinafter being also referred to as cell gap) uniform at least in the display region that is the region contributing to the displaying and to prevent the cell gap from varying even in a case where an external force is applied or external vibrations occur.
The display defects caused by the abnormality of the cell gap mainly include the followings. Specifically, when the cell gap is not kept uniform in the display region, the transmission properties of light becomes different at different positions, thereby causing unevenness in display brightness, which is visually recognized as display unevenness. In addition, when the cell gap varies due to application of an external force or external vibrations, the cell gap is visually recognized as dynamic display unevenness (so-called puddling) that is different at different moments and at different positions in the display region.
The cell gap should be kept uniform in the display region. However, when the cell gap in the peripheral frame region (that is the non-display region adjacent to the periphery of the display region and is hereinafter referred to as non-display region) deviates significantly from the cell gap in the display region or changes, the cell gap especially in the peripheral portion (the vicinity of the peripheral frame region) of the display region is indirectly affected. Consequently, the cell gap in the peripheral portion of the display region cannot be kept in a desired state, thereby interfering with the display characteristics.
Therefore, to prevent the display defects such as display unevenness and puddlings in the display region, the cell gap in the display region and the non-display region needs to be kept uniform and to be prevented from changing.
Conventionally, the following liquid crystal display panel has been disclosed (see, for example, Japanese Patent Application Laid-Open No. 2001-133787). The liquid crystal display panel includes the columnar spacers provided not only in the display region but also in the non-display region and the dummy color material layer (the colored layer formed as the exclusive layer for the columnar resin spacers to be laminated thereon) provided in the portion of the non-display region on which the columnar spacers are to be placed. The color material layer is provided to eliminate the difference in the heights (equalize the heights) of the portions of the substrate surface on which the columnar spacers are to be placed in the non-display region and the display region.
There has been disclosed a method for uniforming the cell gap throughout the entire range of the non-display region and the display region (see, for example, Japanese Patent Application Laid-Open No. 2006-337590). In this method, the shapes of the projections and recesses of the surface formed of the color material layer and the light-shielding layer (black matrix (BM)) are approximated to be identical in the non-display region and the display region, and then, the planarization layer made of, for example, a resin film is formed on the surface.
In Japanese Patent Application Laid-Open No. 2001-133787, by providing the color material layer having the same thickness in the non-display region and the display region, the heights of the portions of the substrate surface on which the columnar spacers are to be placed are set to be equal, which is effective in uniforming the cell gap in the non-display region and the display region. However, the height of the columnar spacers placed in the non-display region and the height of the columnar spacers placed in the display region unfortunately differ from each other.
Specifically, to form the columnar spacers on the substrate side, the color material layer such as the color resist pattern is formed, and then, the resin film formed by applying a resin on the color material layer is patterned by photolithography. If the projections and recesses of the surface serving as an underlayer have different shapes, the resin film unfortunately cannot be formed into the same thickness. Therefore, the resin spacers formed by processing such a resin film also have different thicknesses (heights).
As described above, the projections and recesses of the portions of the surface serving as the underlayer on which the columnar spacers are to be placed have different shapes in the display region in which the openings are to be formed in the light-shielding layer and in the non-display region in which the light-shielding layer is formed overall, whereby the height of the columnar spacers placed in the non-display region and the height of the columnar spacers placed in the display region differ from each other. Particularly, in a case where the resin light-shielding film in which the light-shielding layer is formed to be relatively thick (the light-shielding film formed with the black particles dispersed in the resin) is included, the difference in the shapes of the projections and recesses greatly affects the columnar spacers, causing significant difference in the height of the columnar spacers. Therefore, in the non-display region, the columnar spacers that are identical to the columnar spacers in the display region cannot be formed, whereby the cell gap in the display region and the non-display region cannot be kept uniform nor be prevented from changing. That is, the display defects such as display unevenness and puddling in the display region have not been sufficiently prevented.
Meanwhile, in Japanese Patent Application Laid-Open No. 2006-337590, the arrangement of the columnar spacers is not disclosed. Therefore, if the columnar spacers are not appropriately disposed in the display region and thus the gap between the substrates are not held by the columnar spacers, the cell gap is changed due to application of an external force or external vibrations. Thus, Japanese Patent Application Laid-Open No. 2006-337590 does not disclose at least a method for effectively preventing the display defects such as the puddling caused by application of an external force or external vibrations. Unfortunately, the structure for obtaining overall flattening by using the planarization layer made of, for example, the resin film is relatively costly.